1. Field of the Invention
The Present invention relates to the field of human mandibular prostheses. More particularly, the invention relates to improved prosthetic apparatus for the repair and/or replacement of the condylar process of the human mandible.
2. Description of the Prior Art
The human mandible is a U-shaped bone (lower jaw bone) having a generally horizontal body portion with an anterior prominence (mandibular symphysis) defining the chin in the facial structure. A posterior branch or ramus extends upwardly and rearwardly from each end of the body portion. The upper end of each ramus terminates in a forward coronoid process and a rearward condyloid process or condyle. The condyle is a knob-shaped prominence which fits into a cup-shaped socket known as the glencid fossa formed in the temporal bone of the skull. The condyle, glenoid fossa, and supporting muscle tissue on each side of the skull define a temporomandibular joint (TMJ) which permits the lower jaw to be freely movable.
Surgery in the area of the TM joints of the human mandible frequently involves the necessity of total replacement of the condyle head or entire condylar process of the right or left side or both sides of the mandible. Such surgeries may involve arthroplasty for advanced degenerative TM joint disease, repair and reconstruction of ankylosed TM joints, repair of traumatic fractures of the condyle resulting in loss of normal condylar structure and function, and surgical treatment of congenital hypoplasia of the ramus and condylar process.
A number of types of metallic alloplastic materials have been utilized in the past for mandibular condylar replacements including chrome-cobalt alloys, pure titanium and titanium alloys and stainless steel. In addition, Proplast, Teflon, Silastic, and other synthetic alloplastic materials have been utilized in an effort to obtain maximal function, anatomic reproduction and long life of TM joint replacement protheses. Clinical reports have indicated that metallic condyle replacement prostheses have produced bone loss and erosion of the interfacing surface of the cup-shaped glenoid fossa. Other adverse clinical reports have resulted where Proplast, Teflon and Silastic synthetic materials have been used to form condyle replacement prostheses and such materials have been rejected by the TMJ environment frequently resulting in irreparable harm and damage to the TM joint complex.
In U.S. Pat. No. 3,720,959, granted in 1973 to G. W. Hahn, there is disclosed mandibular prosthetic appliances constructed of malleable metal mesh material, particularly stainless steel mesh fabricated by casting. Where the Hahn mandibular prostheses involve replacement of the condyle such component is fabricated of an acrylic resin material and formed about, and secured to, a metallic mesh body member affixed to the ramus or ramus stump. Over the years the Hahn mandibular prostheses for condyle replacement have been found to be expensive to manufacture and difficult to install and adjust to proper TMJ alignment. Most importantly, such prostheses have experienced unfavorable short-term and long-term biocompatibility and wear resistance of the materials of construction in and under the TMJ environment.
In 1988, T. A. Collins was granted U.S. Pat. No. 4,726,808 disclosing mandibular prostheses comprised of pairs of spaced (substantially parallel) metal strips which are joined together at one end and are placed on opposite sides of mandibular bone stumps that may remain on one side of damaged areas of the mandible. The opposing metal strips are each provided with alternating threaded and non-threaded holes. The non-threaded holes of one strip are oriented so as to oppose the threaded holes of the other strip so that screws can be extended between the strips (through drilled holes of the intermediate mandibular bone) from a non-threaded hole of one strip to a threaded hole of the opposing strip. In one disclosed form, the Collins mandibular prosthesis includes, at the joined end of a set of the parallel metal mounting strips, an attached metallic artificial condyle. A sleeve of silicone or other suitable plastic material is applied over the condyle. It has been well established that Collins-type condyle replacement protheses: are difficult to install because screw hole alignment is not maintained when contouring of the strips is required, provide no means for adjusting the orientation of the condyle head to match the cup-shape of the glenoid fossa, and include condyle head materials that are objectionable in the TMJ environment.
It is an important object of the present invention to provide a mandibular prosthesis for repair and replacement of the condylar process of the human mandible that can be surgically implanted more quickly, easily and safely than the prostheses that are presently available.
It is another important object of the invention to provide a mandibular prosthesis for repair and replacement of the condylar process of the TMJ complex that is constructed of biocompatible materials and can be readily adjusted to proper condyle head orientation with respect to the glenoid fossa.
It is a further object of the invention to provide a mandibular prosthesis for repair and replacement of the condylar process which is of relatively simple and economic construction from materials which have been established as structurally suitable and biocompatible under high stress and force conditions of the type experienced by the TM joint of humans.
Other objects and advantages of the invention will become apparent through the following specification when considered in the light of the attached drawing figures.